This invention relates to a process for the production of a carrierless granular slow release fertilizer composition and to the resulting product.
A variety of processes for producing carrierless granular slow release fertilizer compositions are known and, particularly, processes for producing controlled or slow release reaction products of urea and formaldehyde for fertilizer applications. For example, such carrierless products have been produced by reacting a urea-formaldehyde resin into a solid sheet which is milled and screened to provide a granular product having a desired particle size. A typical U/F mole ratio used for producing the product is in the range of 1.1 to 2.1 and the resulting product contains predominantly long chain methylene urea polymers (i.e., tetramethylene pentaurea (TMPU) and longer chain polymers). Such products and processes are disclosed, for example, in U.S. Pat. No. 3,198,761.
Other known processes for producing carrierless granular slow release fertilizer products are disclosed, for example, in U.S. Pat. Nos. 3,076,700; 3,705,794 and 3,989,470. Essentially, these carrierless products are produced by reacting urea-formaldehyde resins into rigid foams which are dried, milled and screened to the desired granular size. Typical U/F mole ratios used for these processes range from 1.3 to 2.4 and; as opposed to the technology disclosed in U.S. Pat. No. 3,198,761 which is suitable solely for production of nitrogen only products, the processes disclosed in these patents have the flexibility of producing complex fertilizers by slurrying other finely ground additives such as phosphorus and/or potassium salts into the resin prior to the foaming reaction. The products produced by these processes contain predominantly intermediate chain length methylene urea polymers (i.e., trimethylene tetraurea (TMTU) and longer chain polymers).
U.S. Pat. No. 4,025,329 discloses another process for producing a carrierless product. In this process a granular product is formed, for example, in accordance with the disclosures in U.S. Pat. Nos. 3,705,794 and 3,989,470 and then the granules are compacted with other nutrient or pesticide additives to produce a product of uniform composition and particle size. U/F mole ratios employed to produce this slow release product are in a range of 1.3 to 2.4, the density of the granule produced is greater than 1.4 and the granular size is greater then 30 mesh, with substantially all of the granules having a ratio of largest to smallest granule of less than 3:1.
U.S. Pat. Nos. 4,378,238 and 4,411,683 disclose, inter alia, a process for producing carrierless slow release granular products having at least 60% of the polymeric nitrogen in the form of methylene diurea (MDU) and dimethylene triurea (DMTU). The process disclosed therein for producing carrierless product is a two stage process wherein an aqueous mixture of urea, formaldehyde and ammonia is first reacted at elevated temperatures to produce methylol ureas. Then, in a second stage, acid is added directly to the reaction mixture and the acidified mixture is reacted and the condensation reaction product is dried and milled into the final product. Typical U/F mole ratios for these carrierless products range from 1.9 to 2.2.
A further experimental process for producing ureaform fertilizer products is disclosed in an article entitled "Reactions of Molten Urea with Formaldehyde", by Thomas P. Murray et. al., published in Ind. Eng. Chem. Prod. Res. Dev., 1985, at 420-425. The process disclosed therein entails the reaction of molten urea with paraformaldehyde either by mixing paraformaldehyde into melted urea at temperatures of between 130 degrees and 140 degrees C. or by premixing the paraformaldehyde with the urea and heating the solid mixture to 130 degrees C. with stirring. Thereafter, the molten reaction mixture resulting from either of the procedures is cooled to form a solid sheet and the sheet is then ground. U/F mole ratios used under the laboratory-scale conditions described in the publication ranged from 0.5 to 16.2.
However, each of the previously known processes for producing carrierless granular slow release fertilizer products has been found to have certain shortcomings in terms of the physical or chemical characteristics of the products produced thereby and/or the economics of production. For example, the process disclosed in U.S. Pat. No. 3,198,761 is restricted to nitrogen only fertilizers. Furthermore, products produced by this process have been found to demonstrate nitrogen release patterns which are not well suited to certain applications such as turf and short season crops. Similarly, the products resulting from use of the experimental process disclosed in the above referenced article are restricted solely to nitrogen only fertilizer compositions.
The processes disclosed in U.S. Pat. Nos. 3,076,700; 3,705,794 and 3,989,470 represent an advancement in respect to their ability to produce a wide variety of N-P-K minor element ratios in the products and are not restricted to the production of nitrogen only products. However, even these processes are restricted in the range of N-P-K ratios in view of the limit on the amount of solids which can be slurried into the urea-formaldehyde resin without adversely impacting the condensation reaction. Furthermore, the products produced in accordance with the disclosure of U.S. Pat. Nos. 3,076,700; 3,705,974 and 3,989,470 have been found to be quite fragile and dusty.
The process of patent 4,025,329 produces high density granular products of uniform granular size. The process also enables the incorporation of other fertilizer ingredients into the product and provides flexibility as to the N-P-K minor element ratios which can be produced. However, the product does present a dust plume problem resulting from surface adhesion of dust to the product during the manufacturing process when the product is poured from its storage container. Furthermore, the products produced present the same performance problems as noted above in regard to the processes disclosed in U.S. Pat. Nos. 3,076,700; 3,705,794 and 3,989,740. Additionally, these high density products have been found to present a dispersibility problem in regard to their use on turf. In this regard, these products do not disperse adequately to penetrate the turf canopy after application. Thus, the product remains on the surface to be picked up on shoes, golf balls and the like as they travel over the turf.
In regard to the process disclosed in U.S. Pat. Nos. 4,378,238 and 4,411,683 as it relates to carrierless products, it has been found that the process therein cannot be economically or feasibly conducted to produce commercially acceptable carrierless products. Carrierless products as referred to herein are intended to include products which do not employ an absorbent carrier capable of absorbing liquids to provide a granular structure to the final product. That is in carrier based systems, the volume of the product is quite close to the sum of the volumes of the raw materials. This is because the carrier creates the volume structure upon which the product is formed. Thus, the product to feed volume ratio (P/F) for absorbent carrier based fertilizers is essentially 1. Experimental determinations have shown a range of 0.9 to 1.1. Typical examples of commonly used carriers which are not required for use in forming products of the present invention are vermiculite, perlite and corncobs.
Accordingly, none of the prior processes are suitable for producing carrierless granular slow release fertilizer compositions having the desired characteristics either because of process or product shortcomings such as the cost effectiveness of the process, the ability to include additive products in the urea-formaldehyde reaction product and the physical properties of the product. In terms of physical properties, the prior art products have exhibited undesirable characteristics regarding dusting and dispersibility.